Toothed workpieces, particularly toothed wheels, are often pre-cut and are finished by grinding after being heat-treated. The grinding of such teeth with cylindrical grinding worms, which may be dressed, has been shown to be an efficient and cost-saving process. Dressing of such grinding worms is performed with a motor-driven dressing wheel, which is coated with hard-material grains at the working surface (see DE-OS 196 24 842, for example). Thereby the dressing wheel rotates considerably faster than the grinding worm. The dressing wheel passes along the worm path parallel to the grinding worm axis while the grinding worm is running. The longitudinal movement is coupled with the rotation angle of the grinding worm. The grinding worm meshes with the workpiece during the grinding process while the workpiece is moved parallel to its axis. The grinding worm is simultaneously shifted along its axis.
It is the object of the present invention to provide a process and device whereby workpieces, which have been ground with the grinding worm, are optimized in view of their (smooth) running quality.
The invention is based on the fact that the grinding pattern on the tooth flanks are of great significance for the running quality of a ground toothed wheel. Besides contact conditions, topography and roughness of the grinding worm flanks determine the quality of the grinding pattern. The invention is based also on the recognition of the fact that topography and roughness of the grinding worm flanks are subject to periodic fluctuations during a revolution of the grinding worm. In FIG. 1 there are shown, by separating lines, repeating segments 24 of the same topography on the flanks 44 of the grinding worm 20. These fluctuations are caused by the topography of the dressing wheel, which makes a number of revolutions during one revolution of the grinding worm. The dressing wheel actually hasxe2x80x94for technological reasonsxe2x80x94various grain sizes and different grain shapes as well as uneven grain distribution around the circumference, which causes a coating pattern that has a certain regularity in the active profiles. The active profiles cause periodic fluctuations of the topography of the grinding worm flanks during the grinding process, which in turn are reflected as periodic fluctuations of the grinding pattern on the tooth flanks of the workpiece. Through the coupling of the rotation angle of the grinding worm and the dressing wheel, according to the invention, in combination with the related specifically adapted shifting motion, it has been achieved that during the grinding process the periodic fluctuations of the grinding pattern are reproduced onto the workpiece flanks, in combination with the forward feeding motion of the workpiece along its axis, such that a favorable operation of the toothed wheel is obtained. The optimum coupling ratio between the rotation angle of the grinding worm and the dressing wheel may be constant or variable in a controlled manner, depending on the type of gear wheel to be produced. Since there are a number of factors that influence the process, this optimum coupling ratio is determined separately for each gearwheel as appropriate. The once determined optimum ratio is then maintained for the entire workpiece series and is also used the same way in subsequent production series. Thereby the optimum grinding pattern is reproduced with one and the same dressing disc. The same ratio is close to the optimum if another new dressing disc with the same specifications is used for the dressing process.